Button-type batteries are small thin energy cells that are commonly used in watches and other electronic devices requiring a thin profile. A conventional button-type battery includes an anode, a cathode, a porous separator separating the anode and cathode, and an electrolyte within the separator pores.
These internal battery components are housed within a metal casing or housing formed by a lower conductive can and an upper conductive lid. The can is typically in electrical contact with the cathode to form the positive battery terminal, and the lid is in electrical contact with the anode to form the negative battery terminal. The can and lid are crimped or pressed together to form a fluid-tight seal which entirely encloses the anode, cathode, separator, and electrolyte. An electrically insulating sealing gasket is provided within the primary seal between the lid and can to electrically insulate the two housing members.
There is a need in button-type battery usage to make such energy cells thinner. Today, the thinnest commercially available button-type battery has a thickness of 1.2 mm (47.2 mils). It would be desirable to make a thinner battery, particularly one having a thickness of less than 1 mm (39.4 mils). A countering concern, however, is that the integrity of the fluid-tight seal cannot be compromised simply to achieve the goal of thinner batteries.
It is also an objective in button-type battery design to create a housing structure which physically compresses the anode, separator, and cathode together to insure proper operation of the energy cell. This is in some cases accomplished in the prior art by a separate internal spring component which provides desired compressive forces.
It would be desirable to design improved button-type batteries of very thin profile which meet at least one or more of the above stated objectives.
One prior art technique for forming the sealed casing includes separately pre-forming each of the can, lid, and gasket. During assembly, the gasket must be aligned with and inserted into the can. Once the lid is positioned within the can, the can and gasket are crimped about the lid to form the fluid-tight seal. The use of the separate gasket which needs to be preformed and controllably inserted into the can results in increased thickness, higher manufacturing costs and longer assembly times. It would be desirable to enable size reduction, as well as reduce manufacturing costs and assembly time.
U.S. Pat. No. 3,713,896 to Feldhake discloses a technique for dipping the peripheral flange portion of a battery lid into an epoxy resin to form an insulating seal. The epoxy is then cured over time or through thermal techniques. While the Feldhake technique eliminates the separate gasket, it does not improve assembly time due to the lengthy coating and curing steps which also requires handling each part individually. It would therefore be desirable to provide a method for forming a button-type battery which minimizes processing steps and assembly time.